Search results for "Particle physics"
showing 10 items of 6826 documents
πB8B8andσB8B8couplings from a chiral quark potential model
2008
From an SU(2)$\ensuremath{\bigotimes}$SU(2) chiral quark potential model incorporating spontaneous chiral symmetry breaking the asymptotic $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ exchange pieces of the $\mathit{NN}$ potential are generated. From them the $\ensuremath{\pi}\mathit{NN}$ and $\ensuremath{\sigma}\mathit{NN}$ coupling constants can be extracted. The generalization to SU(3)$\ensuremath{\bigotimes}$SU(3) allows for a determination of $\ensuremath{\pi}{B}_{8}{B}_{8}$ and $\ensuremath{\sigma}{B}_{8}{B}_{8}$ coupling constants according to exact SU(3) hadron symmetry. The implementation of the values of the couplings at ${Q}^{2}=0$ provided by QCD sum rules and/or phenomenology m…
Study of heavy-flavor quarks produced in association with top-quark pairs at s=7 TeV using the ATLAS detector
2014
Using a sample of dilepton top-quark pair ((tt) over bar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of (tt) over bar + b + X and (tt) over bar + c + X, collectively referred to as (tt) over bar + HF. The data set used corresponds to an integrated luminosity of 4.7 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF (b or c) quarks in the (tt) over bar sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the (tt) over bar decays a…
Measurement of the D∗± cross section in two photon collisions at LEP
1995
Abstract The inclusive production of D ∗± mesons in photon-photon collisions has been measured by the Aleph experiment at LEP with a beam energy of 45 GeV. The D ∗+ are detected in their decay to D 0 π + with the D 0 observed in three separate decay modes: (1) K − π + , (2) K − π + π 0 and (3) K − π + π − π + , and analagously for the D ∗− modes. A total of 33 events was observed from an integrated luminosity of 73 pb −1 which corresponds to a cross section for Σ( e + e − → e + e − D ∗± X ) of 155 ± 33 ± 21 pb. This result is compatible with both the direct production γγ → c c in the Born approximation and with a more complete calculation which includes both radiative QCD corrections and co…
QCD effects andb-tagging at LEP I
1995
We analyze the impact of usingb-tagged samples in studying non-Abelian effects due to QCD ine + e − → 4jet events at √s=M z 0, using angular variable analyses and comparisons withe + e − → 3jetγ events. We find that QCD effects are largely enhanced inb-quark samples with respect to ‘unflavoured’ ones, where energy-ordering is used to distinguish between gluon and quark jets. We show that theb-quark mass influences the angular distributions significantly and should not be neglected.
Determination of m¯b/m¯c and m¯b from nf=4 lattice QCD+QED
2021
We extend HPQCD's earlier ${n}_{f}=2+1+1$ lattice-QCD analysis of the ratio of $\overline{\mathrm{MS}}$ masses of the $b$ and $c$ quark to include results from finer lattices (down to 0.03 fm) and a new calculation of QED contributions to the mass ratio. We find that ${\overline{m}}_{b}(\ensuremath{\mu})/{\overline{m}}_{c}(\ensuremath{\mu})=4.586(12)$ at renormalization scale $\ensuremath{\mu}=3\text{ }\text{ }\mathrm{GeV}$. This result is nonperturbative. Combining it with HPQCD's recent lattice $\mathrm{QCD}+\mathrm{QED}$ determination of ${\overline{m}}_{c}(3\text{ }\text{ }\mathrm{GeV})$ gives a new value for the $b$-quark mass: ${\overline{m}}_{b}(3\text{ }\text{ }\mathrm{GeV})=4.513(2…
Measurement of soft-drop jet observables in pp collisions with the ATLAS detector at s=13 TeV
2020
Jet substructure quantities are measured using jets groomed with the soft-drop grooming procedure in dijet events from 32.9 fb-1 of pp collisions collected with the ATLAS detector at s=13 TeV. These observables are sensitive to a wide range of QCD phenomena. Some observables, such as the jet mass and opening angle between the two subjets which pass the soft-drop condition, can be described by a high-order (resummed) series in the strong coupling constant αS. Other observables, such as the momentum sharing between the two subjets, are nearly independent of αS. These observables can be constructed using all interacting particles or using only charged particles reconstructed in the inner tra…
Reassessing the discovery potential of theB→K*ℓ+ℓ−decays in the large-recoil region: SM challenges and BSM opportunities
2016
We critically examine the potential to disentangle the Standard Model (SM) and new physics (NP) in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}{K}^{*}{e}^{+}{e}^{\ensuremath{-}}$ decays, focusing on (i) the LHCb anomaly, (ii) the search for right-handed currents, and (iii) lepton-universality violation. Restricting ourselves to the large-recoil region, we advocate a parametrization of the hadronic matrix elements that separates model-independent information about nonperturbative QCD from the results of model calculations. We clarify how to estimate corrections to the heavy-quark limit that would generate a right-h…
Lattice calculation of the pion transition form factor with Nf=2+1 Wilson quarks
2019
We present a lattice QCD calculation of the double-virtual neutral pion transition form factor, with the goal to cover the kinematic range relevant to hadronic light-by-light scattering in the muon $g\ensuremath{-}2$. Several improvements have been made compared to our previous work. First, we take into account the effects of the strange quark by using the ${N}_{f}=2+1$ coordinated lattice simulation gauge ensembles. Second, we have implemented the on-shell $\mathcal{O}(a)$ improvement of the vector current to reduce the discretization effects associated with Wilson quarks. Finally, in order to have access to a wider range of photon virtualities, we have computed the transition form factor …
Gauge-invariant on-shellZ 2 in QED, QCD and the effective field theory of a static quark
1991
We calculate theon-shell fermion wave-function renormalization constantZ 2 of a general gauge theory, to two loops, inD dimensions and in an arbitrary covariant gauge, and find it to be gauge-invariant. In QED this is consistent with the dimensionally regularized version of the Johnson-Zumino relation: d logZ 2/da 0=i(2π)−D e 0 2 ∫d D k/k 4=0. In QCD it is, we believe, a new result, strongly suggestive of the cancellation of the gauge-dependent parts of non-abelian UV and IR anomalous dimensions to all orders. At the two-loop level, we find that the anomalous dimension γ F of the fermion field in minimally subtracted QCD, withN L light-quark flavours, differs from the corresponding anomalou…
QCD corrections to static heavy-quark form factors
2005
Interactions of heavy quarks, in particular of top quarks, with electroweak gauge bosons are expected to be very sensitive to new physics effects related to electroweak symmetry breaking. These interactions are described by the so-called static form factors, which include anomalous magnetic moments and the effective weak charges. We compute the second-order QCD corrections to these static form factors, which turn out to be sizeable and need to be taken into account in searches for new anomalous coupling effects.